Field of the Invention
The present invention relates to an image pickup apparatus, and more particularly, to an image pickup apparatus including a mechanism to move an image pickup element in an optical axis direction.
Description of the Related Art
As a structure to move the image pickup element in the image pickup apparatus, there is known a structure of moving the image pickup element in a plane perpendicular to the optical axis for image stabilization or dust removal. On the other hand, there is known an optical system in which the image pickup element is moved along the optical axis in order to downsize the entire image pickup apparatus or to improve optical performance. For instance, Japanese Patent Application Laid-Open No. 2006-208703 discloses a technology to realize high-precision focus adjustment by moving a focus lens unit in the optical axis direction and afterwards moving the image pickup element in the optical axis direction to a position where a contrast evaluation value reaches a peak.
As one of methods of using the image pickup apparatus by professional users, there is a defocus photography method that does not generate a variation in angle of view by the operation of the optical system.
In this photography method, there is performed an operation of setting a large defocus state and then gradually restoring an in-focus state without changing a composition at focus and zoom positions fixed by a photographer. In particular, in order to avoid an influence of the variation in angle of view due to the operation of the focus lens unit, an optical system for close-up photography is used in many cases.
However, in the conventional technology disclosed in Japanese Patent Application Laid-Open No. 2006-208703, such a defocus operation with a small variation in angle of view can be performed in the image pickup apparatus of the rear focus type, but there is a problem that a sufficient defocus amount (a distance between an imaging position and an image pickup plane) cannot be secured due to a structural limitation, particularly in the telephoto end side of the intermediate zoom region. Therefore, photography of restoring from the large defocus state to the in-focus state can be performed in a vicinity of a wide zoom region, but a defocus state satisfying the photographer cannot be generated in the telephoto end side of the intermediate zoom region so that photography with an image effect intended by the photographer cannot be performed.
In order to solve this problem, it is necessary to physically expand a movement range of the focus lens unit so as to secure the large defocus state in the telephoto end side of the intermediate zoom region, and hence a size of the image pickup apparatus is increased.